This standard specifies the extraction and determination methods of water-soluble phosphorus and available phosphorus content in compound fertilizers, and specifies the calculation method of the percentage of water-soluble phosphorus in available phosphorus. This standard applies to compound fertilizers (including blended fertilizers and various special fertilizers) containing one or more phosphate fertilizers, nitrogen fertilizers, and potash fertilizers, but does not apply to compound fertilizers synthesized by chemical methods such as ammonium phosphate, nitrophosphate fertilizer, and potassium dihydrogen phosphate. GB/T 8573-1999 Determination of available phosphorus content in compound fertilizers GB/T8573-1999 Standard download decompression password: www.bzxz.net

GB/T8573-1999
This standard is a revision of GB/T8573-1988 "Determination of Available Phosphorus Content in Compound Fertilizers". In GB/T8573-1988, different extracting solutions were used to extract available phosphorus from compound fertilizers made from different raw materials of phosphate fertilizers. This revision changed the method to extract with disodium ethylenediaminetetraacetic acid (EDTA) solution. The revised method is simpler and easier to master. From the date of implementation, this standard will replace GB/T8573-1988. This standard was proposed by the Ministry of Chemical Industry of the People's Republic of China. This standard is under the jurisdiction of the National Technical Committee for Standardization of Fertilizers and Soil Conditioners. This standard was drafted by Shanghai Research Institute of Chemical Industry. The main drafters of this standard are: Zhong Fengyuan and Yang Lili. This standard was first issued in 1988.
1 Scope
National Standard of the People's Republic of China
Determination of available phosphorus content for compound fertilizers
Determination of available phosphorus content for compound fertilizersGB/T 8573-1999
Replaces GB/T8573-1988
This standard specifies the extraction and determination methods of water-soluble phosphorus and available phosphorus content in compound fertilizers, and specifies the calculation method of the water-soluble phosphorus to available phosphorus content.
This standard is applicable to compound fertilizers (including blended fertilizers and various special fertilizers) containing one or more phosphate fertilizers and nitrogen fertilizers and potash fertilizers. It is not applicable to compound fertilizers synthesized by chemical methods such as ammonium phosphate, nitrophosphate fertilizer, and potassium dihydrogen phosphate. 2 Referenced Standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard was published, the versions shown were all valid. All standards are subject to revision. Parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T8571—1988 Laboratory sample preparation for compound fertilizers (neqISO/DIS7742.2) HG/T2843--1997 Standard titration solutions, standard solutions, reagent solutions and indicator solutions commonly used in chemical analysis of fertilizer products 3 Principle of the method
Water and sodium ethylenediaminetetraacetic acid (EDTA) solution are used to extract water-soluble phosphorus and available phosphorus in compound fertilizers. The orthophosphate in the extract is ionized and reacts with quinoline phosphomolybdic acid reagent in an acidic medium to form a yellow quinoline phosphomolybdic acid precipitate. The phosphorus content is determined by the quinoline phosphomolybdic acid gravimetric method. 4 Reagents and materials
The preparation of reagents, water and solutions used in this standard shall comply with the provisions of HG/T2843 when the specifications and preparation methods are not specified. 4.1 Ethylaminetetraacetic acid sodium (EDTA) solution, 37.5g/L; weigh 37.5g EDTA in a 1000mL beaker, add a small amount of water to dissolve, dilute with water to 1000mL, and mix well. 4.2 Quinoline molybdate reagent;
4.3 Nitric acid (1+1) solution.
5 Instruments and equipment
Usually used laboratory instruments and:
5.1 Constant temperature drying oven, capable of maintaining 180C±2℃; 5.2 Glass crucible filter, No. 4, volume 30ml.; 5.3 Constant temperature water bath oscillator, a reciprocating oscillator or a gyroscopic oscillator capable of controlling the temperature at 60C±1C. 6 Analysis steps
6.1 Laboratory sample preparation
Approved by the State Administration of Quality and Technical Supervision on June 8, 1999132
Implemented on December 1, 1999
Prepare laboratory samples (generally referred to as test samples) for analysis in accordance with GB/T8571. 6.2 Sample weighing
Weigh a sample containing 100-200 mg of phosphorus pentoxide to an accuracy of 0.0001 g. 6.3 Extraction of water-soluble phosphorus
Weigh the sample in accordance with 6.2, place it in a 75 mL porcelain evaporator, add 25 mL of water to grind, and pour the clear liquid into a 250 mL volumetric flask to which 5 mL of nitric acid solution (4.3) has been added. Continue grinding with water for three times, using 25 mL of water each time, then transfer the water-insoluble matter to the filter paper and wash the water-insoluble matter with water until the solution in the volumetric flask reaches about 200 mL. Finally, dilute with water to the mark and mix well to obtain solution A for the determination of water-soluble phosphorus.
6.4 Extraction of Available Phosphorus
According to the requirements of 6.2, weigh another sample and place it on the filter paper, wrap the sample with the filter paper, and insert it into a 250 mL volumetric flask. Add 150 mL of EDTA solution (4.1) preheated to 60°C, plug the bottle tightly, shake the volumetric flask to disperse the sample in the solution, place it in a constant temperature water bath oscillator (5.3) at 60°C ± 1°C, and oscillate for 1 hour (the oscillation frequency is such that the sample in the volumetric flask can be turned freely). Then take out the volumetric flask, cool it to room temperature, dilute with water to the mark and mix well. Dry filter and discard the initial part of the filtrate to obtain solution B for the determination of available phosphorus. 6.5 Determination of water-soluble phosphorus
Use a single-line pipette to draw 25 mL of solution A and transfer it to a 500 mL beaker. Add 10 mL of nitric acid solution (4.3) and dilute to 100 mL with water. Heat on an electric stove until boiling, remove, add 35 mL of aluminum citric acid reagent (4.2), cover with a watch glass, and gently boil on a hot plate for 1 min or place in a near-boiling water bath to keep warm until precipitation and stratification occur. Remove the beaker and cool to room temperature. Filter with a glass crucible filter (5.2) that has been dried to constant weight in a drying oven at 180°C ± 2°C. First filter out the supernatant, then wash the precipitate 1 to 2 times by pouring, using 25 mL of water each time, transfer the precipitate to the filter, and then wash with water, using a total of 125 to 150 mL of water. Place the precipitate and the filter in a drying oven at 180°C ± 2°C. After the temperature reaches 180°C, dry for 45 min, remove and transfer to a desiccator, cool to room temperature, and weigh.
Blank test
Except for not adding the sample, the same reagents, dosages and analytical steps shall be used as for the sample determination, and the operation shall be carried out in parallel. 6.6 Determination of available phosphorus
Use a single-line pipette to draw 25mL of solution B, transfer it into a 500mL beaker, add 10mL of nitric acid solution (4.3), and dilute to 100mL with water. The following operations shall be carried out according to the analytical steps in 6.5. 7 Expression of analysis results
7.1 Water-soluble phosphorus content (X,) and available phosphorus content (X,), expressed as mass percentage of phosphorus pentoxide (P.0s), are calculated according to formula (1) and formula (2):
X = (ml - m) × 0: 032 07 × 100 = (m - m) × 32. 07mA
X = (m=2m) × 0: 032 07 × 100 = (m: m,) × 32. 07
mg×250
The mass of quinoline phosphomolybdic acid precipitate obtained by measuring water-soluble phosphorus, g; Where: m
m2—The mass of quinoline phosphoaluminate precipitate obtained by blank test when measuring water-soluble phosphorus, g; mThe mass of oxazoline phosphoaluminate precipitate obtained by measuring effective phosphorus, g; When measuring effective phosphorus, the mass of quinoline phosphomolybdic acid precipitate obtained by blank test, g; m, -----
The mass of the sample when measuring water-soluble phosphorus, g; When measuring effective phosphorus, the mass of the sample, g; mB
0.03207—The coefficient for converting the mass of quinoline phosphomolybdic acid into the mass of phosphorus pentoxide. The arithmetic mean of the parallel determination results is taken as the determination result. 1
...(2)
2Allowable difference
GB/T8573—1999
The absolute difference of parallel determination results shall not exceed 0.20%; the absolute difference of laboratory determination results shall not exceed 0.30%. 7.3 The percentage of water-soluble phosphorus in compound fertilizer to available phosphorus (X) is calculated according to formula (3): X,
Where; X,———water-soluble phosphorus content, %; X
Available phosphorus content, %. bzxz.net
1×100
(3))
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